The long-term objective of the research proposed is to develop understanding of growth polarity in eukaryotic organisms through the elucidation of the molecular mechanisms of hyphal growth in the filamentous fungus Neurospora crassa. A class of ten N. crassa ropy mutants has been identified that are defective in normal hyphal growth. One of the genes, ro-1, encodes the heavy chain of cytoplasmic dynein, a microtubule-dependent motor that is required for retrograde transport of vesicles in axons of nerve cells. It is proposed that the remaining phenotypically identical ro mutants identify genes that code for additional subunits or regulators of N. crassa cytoplasmic dynein. The specific objective of this study is to genetically dissect N. crassa cytoplasmic dynein and determine its role in vesicle transport and hyphal growth. The experimental approaches are: (1) molecular analysis of ro-1, the gene encoding cytoplasmic dynein heavy chain; and (2) genetic identification of all ro complementation groups and isolation and characterization of ro genes.